What's old is new again

Robert O'Brien

http://www.boilersondemand.com/

STEVEusaPA

I saw your post on FB about this. He claims total energy consumption of 8-13 watts, but I guess his 'total' doesn't include the burner running.
And he shows pumping into the expansion tank.
I don't see anything that makes it better than an EK. Also, they emphasize proper boiler sizing, but the smallest boiler is 100K.

retiredguy

I do not understand the statement about cheap or low energy consumption without a more detailed explanation. However if you are looking for a system that uses almost no electrical energy you can achieve it with a steam or gravity hot water system that requires no pump and a milli-volt pilot and gas valve combination. Total electrical consumption , none except for that produced by the pilot generator and consumed by the gas valve.

mattmia2

retiredguy said:

I do not understand the statement about cheap or low energy consumption without a more detailed explanation. However if you are looking for a system that uses almost no electrical energy you can achieve it with a steam or gravity hot water system that requires no pump and a milli-volt pilot and gas valve combination. Total electrical consumption , none except for that produced by the pilot generator and consumed by the gas valve.

of course that energy has to come from somewhere and it comes from the fuel and it doesn't distribute or extract as efficiently as carefully designed forced circulation.

ChrisJ

mattmia2 said:

retiredguy said:

I do not understand the statement about cheap or low energy consumption without a more detailed explanation. However if you are looking for a system that uses almost no electrical energy you can achieve it with a steam or gravity hot water system that requires no pump and a milli-volt pilot and gas valve combination. Total electrical consumption , none except for that produced by the pilot generator and consumed by the gas valve.

of course that energy has to come from somewhere and it comes from the fuel and it doesn't distribute or extract as efficiently as carefully designed forced circulation.

I would actually like to see info on this.

How much energy does it take to distribute heat via very low pressure steam vs forced circulated water.

Would be interesting to see how much energy is consumed.
Can that actually be measured?

mattmia2

I am talking more about the transfer from the flue gasses to the water/steam. When you do that at a lower temp and especially when you condense the water in the flue gasses, you transfer more energy from the flue gasses to the water. Unless you hold the system under enough vacuum to make steam around 120 F or lower, steam is going to be inherently about 10% less efficient than a hot water system designed for low temp water.

Hot water vs hot water may be a little closer.

ChrisJ

mattmia2 said:

I am talking more about the transfer from the flue gasses to the water/steam. When you do that at a lower temp and especially when you condense the water in the flue gasses, you transfer more energy from the flue gasses to the water. Unless you hold the system under enough vacuum to make steam around 120 F or lower, steam is going to be inherently about 10% less efficient than a hot water system designed for low temp water.

Hot water vs hot water may be a little closer.

Ok,
I still want my question answered.

RayWohlfarth

@ChrisJ On residential steam systems they are designed for a one ounce steam pressure drop for every one hundred feet. Commercial is about double that. Steam can zoom around a building for only a couple ounces of steam pressure and the condensate is returned by gravity

ChrisJ

RayWohlfarth said:

@ChrisJ On residential steam systems they are designed for a one ounce steam pressure drop for every one hundred feet. Commercial is about double that. Steam can zoom around a building for only a couple ounces of steam pressure and the condensate is returned by gravity

My own system runs at 1/4 of an ounce most of the time.
But that is still energy being consumed. Nothing is free.

Using a percentage of a 125,000 btu/h burner to move the fluid is a bit hard to notice vs a tiny electric pump. It's easy to measure what the pump uses.

mattmia2

I think the pump allows you to get more efficiency of transfer, both of system fluid and of flue gas that doesn't have enough leftover heat to move on its own than the energy in those fluids used to move them. This really seems like something someone worked out in the 1930's or so.

ChrisJ

mattmia2 said:

I think the pump allows you to get more efficiency of transfer, both of system fluid and of flue gas that doesn't have enough leftover heat to move on its own than the energy in those fluids used to move them. This really seems like something someone worked out in the 1930's or so.

I'm not so sure of that.

Making assumptions is bad. We need tests.
There'a also practicality that needs to be considered. Efficiency isn't the only thing.

Steamhead

mattmia2 said:

I am talking more about the transfer from the flue gasses to the water/steam. When you do that at a lower temp and especially when you condense the water in the flue gasses, you transfer more energy from the flue gasses to the water. Unless you hold the system under enough vacuum to make steam around 120 F or lower, steam is going to be inherently about 10% less efficient than a hot water system designed for low temp water.

Hot water vs hot water may be a little closer.

The other side of this is, a steam system involves far less water than a hot-water system. So there's less water to heat in the first place.

ChrisJ said:

Making assumptions is bad. We need tests.

Amen. And as far as I know, there has never been a head-to-head, scientifically done test of a steam system in the best possible condition versus a hot-water system in equally good condition. Hot-water guys seem to like to trumpet their alleged better efficiency, but we've gotten similar efficiency gains just by fixing the steam.

Here is but one example:

https://forum.heatinghelp.com/discussion/145002/actual-savings-over-steam-heating

ratio

ChrisJ said:

Efficiency isn't the only thing.

Now that's just crazy talk. Something more important than efficiency? What next, are you going to try and tell me that newer isn't better?

Feel free to click on "LOL" below

RayWohlfarth

I would love to see a comparison of the two. I know RPA did a comparison of the VRF costs in comparison to hydronic and hydronic was much lower.

Robert O'Brien

ChrisJ said:

I think the pump allows you to get more efficiency of transfer, both of system fluid and of flue gas that doesn't have enough leftover heat to move on its own than the energy in those fluids used to move them. This really seems like something someone worked out in the 1930's or so.

I'm not so sure of that. Making assumptions is bad. We need tests. There'a also practicality that needs to be considered. Efficiency isn't the only thing.

Three hypothetical situations

1. Hot water boiler @ 180F

2. Steam boiler @ 212F

3. Hot water boiler @ 140F

All else being equal, what would the combustion efficiency of each be?

ChrisJ

Robert O'Brien said:

ChrisJ said:

mattmia2 said:

I think the pump allows you to get more efficiency of transfer, both of system fluid and of flue gas that doesn't have enough leftover heat to move on its own than the energy in those fluids used to move them. This really seems like something someone worked out in the 1930's or so.

I'm not so sure of that.

Making assumptions is bad. We need tests.
There'a also practicality that needs to be considered. Efficiency isn't the only thing.

Three hypothetical situations

1. Hot water boiler @ 180F

2. Steam boiler @ 212F

3. Hot water boiler @ 140F

All else being equal, what would the combustion efficiency of each be?

Two hypothetical situations which may actually answer my question.

1: Steam boiler at 140F
2: Hot water boiler at 140F.

All else being equal what would the combustion efficiencies of each be?

hot_rod

There are a few efficiencies that need to be considered together
Efficiency being desired output quantity divided by necessary input.
Steady state heat output divided by energy input rate

Combustion efficiency both steady state and cycle efficiency, determined by combustion analysis.
Cycle efficiency goes south on low load days with fixed speed boilers.

I believe a modulating boiler wins on all accounts, all things being equal.

Didn't Brookhaven drill down cycle efficiencies years back?

Add Category 3, being HW boiler operating at 120°

ratio

How does required maintenance factor in? Repairs?

Steamhead

Robert O'Brien said:

Three hypothetical situations

1. Hot water boiler @ 180F

2. Steam boiler @ 212F

3. Hot water boiler @ 140F

All else being equal, what would the combustion efficiency of each be?

According to Wikipedia, the adiabatic temperature of a natural gas flame is 3,542° F, and that of a light fuel oil (which I believe is same as #2) flame is 3,820° F:

https://en.wikipedia.org/wiki/Adiabatic_flame_temperature

So, based on this, a difference of 72° F of the fluid on the other side of the heat exchanger will only make a miniscule difference in efficiency.

mattmia2

Steamhead said:

Robert O'Brien said:

Three hypothetical situations

1. Hot water boiler @ 180F

2. Steam boiler @ 212F

3. Hot water boiler @ 140F

All else being equal, what would the combustion efficiency of each be?

According to Wikipedia, the adiabatic temperature of a natural gas flame is 3,542° F, and that of a light fuel oil (which I believe is same as #2) flame is 3,820° F:

https://en.wikipedia.org/wiki/Adiabatic_flame_temperature

So, based on this, a difference of 72° F of the fluid on the other side of the heat exchanger will only make a miniscule difference in efficiency.

It definitely makes a big difference if you condense the heat of vaporization out of the water in the combustion product.

Not sure of the non-condensing case. it seems like the excess air and the mixture being much cooler when it contacts the hx factors in somehow.

Steamhead

mattmia2 said:

Steamhead said:

Robert O'Brien said:

Three hypothetical situations

1. Hot water boiler @ 180F

2. Steam boiler @ 212F

3. Hot water boiler @ 140F

All else being equal, what would the combustion efficiency of each be?

According to Wikipedia, the adiabatic temperature of a natural gas flame is 3,542° F, and that of a light fuel oil (which I believe is same as #2) flame is 3,820° F:

https://en.wikipedia.org/wiki/Adiabatic_flame_temperature

So, based on this, a difference of 72° F of the fluid on the other side of the heat exchanger will only make a miniscule difference in efficiency.

It definitely makes a big difference if you condense the heat of vaporization out of the water in the combustion product.

Not sure of the non-condensing case. it seems like the excess air and the mixture being much cooler when it contacts the hx factors in somehow.

But in order to condense, you must remove the exhaust mechanically, rather than using a standard chimney. An exhauster/draft fan/power venter uses energy and moving parts which will require service. A chimney uses neither.

Robert O'Brien

All else being equal, stack temp is going to rise degree for degree with boiler water temperature, putting steam at an insurmountable disadvantage. Never mind the combustion losses on the energy required to cause the liquid to vapor state change.

PerryHolzman

The other possible factor on your 140F steam vs hot water...

How much energy for the vacuum pump on the steam system.

This may turn out to be about equal to the energy to circulate water. However, a gravity hot water system would have no circulating pump - but cost more to build due to the larger pipes.

In the end its not just about efficiency. It's about cost to build, and cost to maintain, in addition to cost to operate.

That's why my 2007 Vitodens 200 installation may be great for efficiency; but, overall not the lowest cost to operate and maintain system (as I have learned).

Have a great day,

Perry

mattmia2

In theory a steam system could make its own vacuum assuming it was perfectly sealed. Of course you would need some way to regulate the vacuum and the setpoint based on the vacuum to keep it steaming until it expelled all the air and cooled and made a vacuum.

Perhaps the vacuum pump falls in to the same category as the inducer fan where it uses some energy but not as much as the alternative especially when drafting in already heated air to naturally vent the appliance is figured in.

Another factor is not necessarily designing the moving parts for long term durability but rather for cost in more complex systems.

ChrisJ

Robert O'Brien said:

All else being equal, stack temp is going to rise degree for degree with boiler water temperature, putting steam at an insurmountable disadvantage. Never mind the combustion losses on the energy required to cause the liquid to vapor state change.

There is literally zero energy required to change liquid to vapor.  You get 100% back when the steam condenses back.   Vacuum can easily be used to lower the boiling point to 120 degrees.

The comments about a huge amount of energy required to change water into steam are correct. However none of it is lost.  It's a benefit and heat pumps use the same thing.

jumper

Presumption that lower temperature media invariably requires less fuel is not accurate. One can recuperate exhaust energy to preheat combustion air.

Gravity circulation also does not necessarily waste energy. After all where does the waste end up?

There's also comfort consideration. A room with steam radiator at 200° may be more comfortable at lower air temperature than one warmed with 120° terminal.

If energy cost is so important consider an undersized steam system that keeps your home at 55° and then have individual electric radiant heaters to be turned on when occupied. Also acquire comfortable sweaters and hats.

hot_rod

ChrisJ said:

Robert O'Brien said:

All else being equal, stack temp is going to rise degree for degree with boiler water temperature, putting steam at an insurmountable disadvantage. Never mind the combustion losses on the energy required to cause the liquid to vapor state change.

There is literally zero energy required to change liquid to vapor.  You get 100% back when the steam condenses back.   Vacuum can easily be used to lower the boiling point to 120 degrees.

The comments about a huge amount of energy required to change water into steam are correct. However none of it is lost.  It's a benefit and heat pumps use the same thing.




Is there such a thing a 100% in any heat exchange? Wouldn't that be perpetual motion

Robert O'Brien

ChrisJ said:

Robert O'Brien said:

All else being equal, stack temp is going to rise degree for degree with boiler water temperature, putting steam at an insurmountable disadvantage. Never mind the combustion losses on the energy required to cause the liquid to vapor state change.

There is literally zero energy required to change liquid to vapor.  You get 100% back when the steam condenses back.   Vacuum can easily be used to lower the boiling point to 120 degrees.

The comments about a huge amount of energy required to change water into steam are correct. However none of it is lost.  It's a benefit and heat pumps use the same thing.

It's not all recouped. Combustion efficiency losses. 

ChrisJ

Robert O'Brien said:

ChrisJ said:

Robert O'Brien said:

All else being equal, stack temp is going to rise degree for degree with boiler water temperature, putting steam at an insurmountable disadvantage. Never mind the combustion losses on the energy required to cause the liquid to vapor state change.

There is literally zero energy required to change liquid to vapor.  You get 100% back when the steam condenses back.   Vacuum can easily be used to lower the boiling point to 120 degrees.

The comments about a huge amount of energy required to change water into steam are correct. However none of it is lost.  It's a benefit and heat pumps use the same thing.

It's not all recouped. Combustion efficiency losses. 

Any energy consumed in going from liquid to vapor is 100% recouped.

Combustion losses are a separate subject.

Robert O'Brien

ChrisJ said:

ChrisJ said:

Robert O'Brien said:

All else being equal, stack temp is going to rise degree for degree with boiler water temperature, putting steam at an insurmountable disadvantage. Never mind the combustion losses on the energy required to cause the liquid to vapor state change.

There is literally zero energy required to change liquid to vapor.  You get 100% back when the steam condenses back.   Vacuum can easily be used to lower the boiling point to 120 degrees.

The comments about a huge amount of energy required to change water into steam are correct. However none of it is lost.  It's a benefit and heat pumps use the same thing.

It's not all recouped. Combustion efficiency losses. 

Any energy consumed in going from liquid to vapor is 100% recouped. Combustion losses are a separate subject.

Separate subject? No, they're on the same bill!  I guess the increased idle loss from having a boiler stop every cycle at 212F+ isn't germane either?  Pointing out the incontrovertible fact that a steam system can never be as efficient as a hot water system isn't the same as advocating for their demise. 

Steamhead

ChrisJ said:

Any energy consumed in going from liquid to vapor is 100% recouped.

Combustion losses are a separate subject.

That's correct. Also, losses in circulator pumps, draft fans/inducers, etc. This all figures into total system efficiency.

It is a mistake to focus on one component, such as a boiler, and ignore losses elsewhere in the system.

Total system efficiency is part of total cost of ownership (TCO) which takes into account all the costs needed to operate and maintain a system.

Jamie Hall

Somewhere back up there somebody (yes, I could go back and look for it. No, I'm not going to) smacked the nail dead centre: the only correct, valid way to compare various systems is to determine the total energy input -- fuel, electricity, etc. to total usable energy output: heat, in our case, delivered to the space. Anything else, looking only at combustion or circulation or whatever, is not going to be real.

Further, one has to specify rather carefully all the various conditions.

I don't think it has been done... or if it has, only for a rather limited set of conditions.

That said, there are some good points. Perhaps the most important is that if -- and only if -- one can cool the exhaust gas down to the point where most of the water vapour from combustion is condensed, one can obtain close to the higher heating value of the fuel. For natural gas, about 22,400 BTU per pound. For light fuel oil, 18,900 BTU per pound. If the flue gas stays about the condensation temperature, then you can only get the lower heating value -- 20,300 BTU per pound and 17,500 BTU per pound, respectively. Thus if you can,t condense, you can get about 90% as much heat out of a pound of natural gas and about 93% as much heat out of a pound of fuel oil (the difference is that fuel oil produces less water vapour per BTU released than natural gas does. Playing with the numbers a little more, that means that a natural gas burner which reaches 86% efficiency non-condensing could, in principal, reach 96%, fully condensing, while an oil burner, also at 86% non-condensing, could reach about 93%.

But. That makes the blythe assumption that you can cool the flue gas to the point where all the water vapour is condensed. It is quite true that 140 F is taken as a sort of magic number for that -- but that isn't actually cool enough to get the full benefit. Probably around 90 F is more like it.

Condensing oil burners are rather rare in heating, for a very good reason: while condensed combustion gas from natural gas is corrosive, it's not that bad. Fuel oil, however, unless you an guarantee ultra low sulfur content, is pretty fierce.

Of course, one problem is that when a heating system is running hardest, it is least likely to be able to condense unless there is a lot of radiation. In any event, a single point measurement of efficiency of combustion really isn't that much more helpful than the mileage stickers on new car windows...

Another item. Someone up there mentioned the energy required to circulate steam, with the thought that it was hard to measure. Actually, not. Suppose we have a nice steam system in good shape which runs on a differential pressure of 4 ounces per square inch. Further, let us suppose that the system creates 385 pounds of steam per hour. Applying some rather dubious mathematics, that comes out to somewhere in the neighbourhood of 2 times 10 to the negative 4 power horsepower -- 0.0002 hp -- to power the circulation. Engineers hate the term "negligible", but truly... that is negligible. The figure for gravity hot water will be higher, but still negligible.

This feeds into the question of gaining efficiency in a steam system by running it at a vacuum -- say, low enough to get to that magic 140 number. Unless the vacuum can be naturally created, the power to run the vacuum pump will be several orders of magnitude greater (it's still small -- the overall efficiency will be greater under a vacuum -- but then runs into the problem of increased maintenance... and capital cost.. which is another factor altogether).

(somewhat off topic: marine steam turbines typically do run under a natural vacuum, obtained not from condensing the flue gas but from condensing the steam in heat exchangers against sea water -- and the sea water temperature, then, has an effect on the maximum power that the turbines can create)

Anyway. All very interesting. In an academic way. In a practical way in Joe Sixpack's house? I personally think that other factors -- capital costs, maintenance, reliability among them -- are more important than some efficiency numbers. Always assuming that the system is tuned that that particular system can be, of course.

The Steam Whisperer

To address the supposedly much higher efficiencies of hot water versus steam I give you the data from some of the only boilers I have seen that have published seperate heat outputs for both steam and water versions of the same boilers. The Peerless 64 series is tested using ANSI standards To take the biggest model, 633,000 input hot water output 525,000 (82.94%), steam output 506,000 (79.93%) and the lowest input 345,000, hot water 286,000 ( 82.9%) and steam 274,000 ( 79.42%). We're talking only a 3 % difference.
Once again this idea that since it takes so much more energy to boil water, that steam must be so much less efficient is complete bunk. Heat of vaporization is all returned during condensation in the system. If this wasn't true, condensing hot water boilers would have no efficiency gain over non condensing boilers. The vaporized moisture in the combustion process would be useless if this energy could not be captured during the condensing process. In addition, compressor driven air conditioning systems would not work.
Also energy used for circulation is not lost, it is converted into heat by friction with the piping system. However, using natural gas to power circulation, as in steam, is inherently more efficient than using electricity. Overall grid efficiency of natural gas burned on site is about 82%, overall efficiency of the electrical grid is about 30%. In addition, I would suspect that the energy used to move steam is far less than a modern hot water system uses. Of course, it is likely the steam system has more embodied energy invested in its installation than a modern hot water system, but it appears it may also last way longer.

The problem of energy used for circulation is probably one of the main driving factors for ducted cooling systems disappearing from the world wide market. The huge fans for ducted systems use large amounts of electricity and at the same time convert that energy into heat inside the system. This additional heat must be overcome by the cooling system. This contributes to window A/C having an inherent efficiency advantage over ducted central system.... the window A/C blower motor is outside, not inside warming the air. There is some fictional heating, but the big source of heat, the fan motor is cooled at the exterior side of the system.

When looking at vacuum, it has to be remembered that once a vacuum is drawn it never disappears, unless there are leaks. We have a number of 1920's systems that use either vacuum pumps or natural vacuum, and those systems can hold vacuum often for days. The power draw to maintain vacuum in a system in good working order is again, to use jamie's term, negligable, since the vacuum pump rarely runs.

jumper

Forgive me for repeating that one can recuperate exhaust energy to preheat combustion air. So you can harvest more heating value when outside air is colder.And there are additional methods to utilize flue heat. The big disadvantage of most steam heating is that it requires some knowledge and attention. But modern properly engineered steam is overwhelmingly superior to HHW.

The Steam Whisperer

Jumper.... The original Dunkirk Quantum boiler did that. It had a heat exchanger for the exhaust that transferred both heat and moisture to the intake and had a primary condensing heat exchanger. On days with a 115F supply water temp, the exhaust temp was in the only in the upper 90's. Really efficient heat transfer, but required an inducer fan, primary pump, condensate pump ( to transfer hot exhaust condensate to spray into the intake air) and the electronic controls to run it. It did knock off about $250.00 per year in gas costs from my 1966 American standard gas atmospheric (270,000 input running on 90,000 input from 3 of the 9 burners), but my electric use went up a bunch.

Also the Art Institute in Downtown Chicago has added Heat Sponge heat recovery heat exchangers to its 2 primary steam boilers and they run around 92%, IIRC. I'm not sure what its using for a transfer medium. I've priced heat exchangers like that for 1Million btu boilers and you can't get a whole lot of efficiency gain with using returning condensate ( on many of my 2 pipe systems the return condensate is almost never above 80F) because the pumped water volume is so low. Combustion air preheat, maybe another thing I need to look into. It would be nice if I could use the returning condensate as the heat transfer medium and heat the condensate and combustion air at the same time.

My most advanced 2 pipe systems all run outdoor reset of boiler input with mod gas power burners, so most of the year the boilers are already running in the mid 80's efficiency ( cast iron sectionals). Exhaust temps are already down to 350 to 375F with 30% or less excess air. ( they run tighter at higher inputs.) Our 1920's steel firetubes ( Kewanees and Pacifics) run around 85% year round for steam. They have really big heat transfer surfaces in the main firebox... especially the Pacifics. None of the new boilers have that much heat transfer surface so they are not as efficient as these old boilers.

jumper

>>None of the new boilers have that much heat transfer surface so they are not as efficient as these old boilers<<

Certainly old steel & CI fire tube boilers lasted longer. In the olden days when North America had industry sometimes we used direct contact heat extractors. Perhaps 98% of HHV when there was a use for warm slightly acidic water. I forget how big the recirc and the pressure pumps were.